Dear Asma,
It is really appreciable that you are so conscious about your friend. It means that your friend is lucky enough as she got such a careful friend like you. According your words you are best friends and best friend is really a well-wisher of the other. Now if you find a way out to solve her problem of being serious towards studies and improving her attitude, it would be beneficial for her. Tell her in isolation that if she pays attention towards her studies, she could be a pretty girl in the eyes of her parents and her teachers as well. Tell her that every person has his or her own personality therefore try to develop good and acceptable habits in her. Insha Allah this will work.